The invention discloses a fishing boat tail gas refrigerating unit, which adopts the principle of ammonia-water absorption refrigeration and uses the waste heat of fishing boat tail gas to drive a system to work so as to finally realize a refrigeration process. The refrigerating unit realizes low temperature, high efficiency and high power. The system mainly comprises a generating and rectifying device, a condenser, an ammonia throttle valve, a liquid storage tank, an evaporator, an absorber, a solution pump, a solution throttle valve, a solution heat exchanger and the like. Aqueous solution of ammonia is heated at a generating part of the generating and rectifying device to evaporate a large amount of ammonia vapor and a small amount of water vapor, the water vapor is rectified at a rectifying part of the generating and rectifying device, the rest ammonia vapor is condensed in the condenser to form liquid ammonia, the liquid ammonia is throttled and decompressed by the throttle valve and then enters the liquid storage tank, and the liquid ammonia is evaporated and refrigerated in the evaporator to provide cold energy for fresh keeping for a fishing boat. The refrigerating unit reduces the ice load of the fishing boat, effectively improves the freshness of fishes, and has significance for realizing energy conservation and emission reduction on the fishing boat.